#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <string>
#include <vector>
#include <queue>
#include <utility>

typedef std::pair<int, int> P;
struct edge {int to, cap, cost, rev; };

int const MAX_V = 117;
int const INF = 1<<27;
int V;
std::vector<edge> G[MAX_V];
int h[MAX_V];
int dist[MAX_V];
int prevv[MAX_V], preve[MAX_V];

void add_edge(int from, int to, int cap, int cost)
{
	G[from].push_back((edge){to, cap, cost, (int)G[to].size()});
	G[to].push_back((edge){from, 0, -cost, (int)G[from].size() - 1});
}

int min_cost_flow(int s, int t, int f)
{
	int res = 0;
	std::fill(h, h + V, 0);
	while (f > 0) {
		std::priority_queue<P, std::vector<P>, std::greater<P>> que;
		std::fill(dist, dist + V, INF);
		dist[s] = 0;
		que.push(P(0, s));
		while (!que.empty()) {
			P p = que.top(); que.pop();
			int v = p.second;
			if (dist[v] < p.first) continue;
			for (int i = 0; i < (int)G[v].size(); i++) {
				edge & e = G[v][i];
				if (e.cap > 0 && dist[e.to] > dist[v] + e.cost + h[v] - h[e.to]) {
					dist[e.to] = dist[v] + e.cost + h[v] - h[e.to];
					prevv[e.to] = v;
					preve[e.to] = i;
					que.push(P(dist[e.to], e.to));
				}
			}
		}
		if (dist[t] == INF) return -1;
		for (int v = 0; v < V; v++) h[v] += dist[v];

		int d = f;
		for (int v = t; v != s; v = prevv[v])
			d = std::min(d, G[prevv[v]][preve[v]].cap);
		f -= d;
		res += d * h[t];
		for (int v = t; v != s; v = prevv[v]) {
			edge & e = G[prevv[v]][preve[v]];
			e.cap -= d;
			G[v][e.rev].cap += d;
		}
	}
	return res;
}

int main()
{
	std::ios::sync_with_stdio(false);
	int n, m;
	while (std::cin >> n >> m) {
		int s = 0, t = n + 1;
		V = t + 1;
		for (int i = 0; i <= V; i++) G[i].clear();
		int sum_in = 0, sum_out = 0;
		for (int i = 1, a, b; i <= n; i++) {
			std::cin >> a >> b;
			sum_in += a; sum_out += b;
			add_edge(s, i, a, 0);
			add_edge(i, t, b, 0);
		}
		for (int i = 0, x, y; i < m; i++) {
			std::cin >> x >> y;
			add_edge(x, y, INF, 1);
			add_edge(y, x, INF, 1);
		}
		if (sum_in != sum_out) {
			std::cout << "-1\n";
			continue;
		}
		int ans = min_cost_flow(s, t, sum_out);
		std::cout << ans << '\n';
	}
}

